Try this 'hand-eye coordination' brain exercise!
To keep your mind sharp as you get older, try this trick from Dr. Ian Robertson at the Center for Brain Health at the University of Texas: Bounce a tennis ball against a wall, and catch it with one hand… then, try the other. Or bounce a ping-pong ball on a paddle. That works your hand-eye coordination and gives your brain a good workout. And the smaller the ball, the harder your brain will work.